In many applications, it is desirable to be able to provide a viewer of a scene with additional visual information. For example, an aircraft pilot may be equipped with goggles which permit direct viewing of a scene while superimposing data, for example concerning airspeed, altitude and so on, from a display using a suitable arrangement of prisms and other optical components to conduct it to the focal plane. In other arrangements, the scene may be viewed via an image intensifier, for example, which may convert infra-red radiation into the visible part of the spectrum and intensify low level visible radiation. It may also be advantageous to provide additional symbology overlaid on an intensified image of the scene.
The present invention is applicable to both applications in which a scene is viewed directly by an observer, with or without enhancements provided by an optical assembly, and for those in which the viewed scene is representative of the actual scene and has been subjected to processing by an image intensifier tube or some other device.